1. Field of the Invention
The present invention relates to a clasp for a chain, including a casing, a locking member resiliently supported in the casing and movable from a closed into an open position, a spring member coupled to the locking member and operative to maintain the locking member in its closed position, which casing is a flat shaped article bent to a U-form, which locking member has the shape of a flat plate and is pivotable between the flank sections of the casing around a pin located at a central area of the casing, has one end formed to have the shape of a hook, the opening of which being closed off by an edge section of the casing, and has an eyelet provided at the end opposite of the hook, the locking member having further a projection projecting out of the casing and acting as operating member for inducing the opening movement of the hook.
2. Description of the Prior Art
Clasps for chains are available in numerous various designs. Best known and available worldwide is the so-called spring-ring clasp. This spring-ring clasp comprises a casing manufactured from a tube and bent to the shape of an open ring, in which casing a ring shaped closure member is supported resiliently. The drawback of this worldwide known clasp is that under certain circumstances it will open unintentionally if the chain is subjected to a pulling force. Moreover, this known clasp is relatively expensive to manufacture and can be operated, i.e. opened only by the aid of a fingernail.
A sheet metal snap hook is disclosed in the U.S. Pat. No. 2,166,666. This sheet metal snap hook comprises a spiral spring which biasses the hook into its closing position and, moreover, is not provided with any operating member allowing an easy and safe blind operating of the snap hook when designed on a small scale, for instance, for use as snap hook for a jewelry chain. The jewelry clasp of the U.S. Pat. No. 4,458,393 comprises also a spiral biassing spring and is rather difficult to operate because a shoulder portion for pivoting its hook member must be given a pivoting pressing movement which again is rather difficult to induce if the clasp is designed in small dimensions as common by jewelry.
In the U.S. Pat. No. 2,544,147 discloses a clasp having a prong section biassed by a resilient portion into its closed position. The prong is operated by a lug for inducing a pivoting movement of the prong. Again, a pivoting movement must be made for operating the prong and, moreover, the prong is in no way protected against an obliquely attacking pulling force such that when subjected to a pulling force this clasp can open itself.
The French patent specification FR-PS No. 1.503.850 illustrates a clasp for, for instance, bracelets, chains etc. which has a pivotably supported double ended hook member. This hook member is not biassed into a closed position and, therefore, will open quite easily, specifically if the pulling force exerted thereon by e.g. a chain does not act exactly in the direction of the center axis of this clasp. Also, this clasp is rather difficult to operate blindly, for instance, when located at the neck of a bearer of a jewelry chain.